The present application relates to a self-luminous display such as an organic electroluminescence (EL) display and an electronic system including the display.
A display device having higher performance has been demanded with development of the information and communication industry. For example, each of an organic electroluminescence (EL) display, an inorganic EL display, and a field emission display (FED) is a display including a self-luminous display device, and has been notified as a next-generation display due to its wide viewing angle, high contrast, and high response speed. For example, the organic EL device includes a lower electrode, a light emitting layer, an upper electrode, and a counter substrate in order of closeness to a drive substrate, and is roughly classified into a bottom emission type where display light is extracted through the drive substrate, and a top emission type where display light is extracted through the counter substrate.
A technique of the self-luminous display, in which a reflective section is provided on a side opposite to a display surface with respect to the light emitting layer, has been proposed in order to efficiently extract light emitted from the light emitting layer. For example, in the case of the top emission type, the lower electrode is configured of a light-reflective metal such as aluminum (Al), silver (Ag), or an alloy of such a metal so as to serve as the reflective section. This enables extraction of reflected light, as display light, of light emitted from the light emitting layer to a direction of the lower electrode, in addition to light directly emitted from the light emitting layer to a direction of the counter electrode.
However, the reflective section also reflects outside light entering through the display surface, which may reduce effective contrast, leading to a reduction in image quality and in visibility. In particular, this greatly affects the image quality and visibility during use of the display in the open. There has been provided a configuration, in which a circularly polarizing plate is provided on a display surface side of the counter substrate, in order to suppress such reflection of outside light. The circularly polarizing plate includes an absorption-type polarizing plate combined with a quarter retardation film. In the display including the circularly polarizing plate, outside light entering through the display surface passes through the absorption-type polarizing plate, and thus changes into linear polarization that then passes through the quarter retardation film. The linear polarization passes through the quarter retardation film and thus changes into circular polarization. The circular polarization is then reflected by the reflective section (lower electrode), and then passes through the quarter retardation film again and thus changes into linear polarization. The linear polarization, which has passed through the quarter retardation film two times, is shifted in phase by λ/2 with respect to the linear polarization before the first action of passing through the quarter retardation film. Hence, the linear polarization does not go to the display surface but is absorbed by the absorption-type polarizing plate.
According to the above mechanism, the circularly polarizing plate substantially perfectly suppresses reflected light of outside light. However, the circularly polarizing plate greatly attenuates light emitted from the light emitting layer. As a result, light output is reduced, leading to an increase in power consumption and a reduction in life due to an increase in current density. For example, light transmittance of the circularly polarizing plate is about 40%. To address such a difficulty, a technique has been proposed, in which a reflection-type polarizing plate having the same light-axis direction as that of an absorption-type polarizing plate is interposed between the absorption-type polarizing plate and the quarter retardation film in order to improve light output (for example, Japanese Unexamined Patent Application Publication Nos. 2010-243769 and 2001-357979). In this technique, among light emitted from the light emitting layer, light, which has a light-axis direction orthogonal to that of the reflection-type polarizing plate or the absorption-type polarizing plate, is reflected by the reflection-type polarizing plate and the reflective section in this order, and thus passes through the quarter retardation film two times. Consequently, the light is shifted in phase by λ/2, and extracted through the display surface. As a result, light output increases to twice the square root (√) of light transmittance (in a parallel direction) of the absorption-type polarizing plate, or about 90% of light emitted from the light emitting layer.